Chapter Six

Definition Worksheet #8: Chapter 6
Define the following terms related to energy and metabolism.
1. Activation Energy
Minimum amount of energy required to start a reaction; enzyme action lowers this energy barrier.
2. Active Site
Crevice in an enzyme molecule where a specific reaction is catalyzed
3. Anabolism
The phase of metabolism in which simple substances are synthesized into the complex materials of living tissue.
4. Catabolism
The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy.
5. Co-Enzymes
Small molecules that take part in an enzymatic reaction and is reversibly modified during the reaction.
6. Co-Factors
An inorganic complement of an enzyme reaction, usually metal ions.
7. Competitive Inhibition
An inhibitory effect on a metabolic function, such as an enzyme, not based on competition for the binding site of the naturally occurring substrate, but on a different effect on the molecule whose function is being inhibited.
8. Endothermic Reactions
A chemical reaction that takes up heat. This type of reaction requires energy input to progress. The products have MORE energy than the REACTANTS.
9. Exothermic Reactions
A chemical reaction that releases heat. This type of reaction releases energy, the reactants have more energy than the products, because there is energy released!
10. First Law of Thermodynamics
A law of nature; states that the total amount of energy in the universe remains constant; energy can be converted from one form to another, but it cannot be created or destroyed.
11. Kinetic Energy
The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its speed.
12. Noncompetitive Inhibition
Inhibition of enzyme activity by substances that combine with the enzyme at a site other than that utilized by the substrate.
13. Oxidation Reactions
Reactions in which electrons are given to another molecule (oxidation is loss of electrons, coupled with a reduction which is gain of electrons).
14. Phosphorylation Reactions
An enzyme-mediated transfer of a phosphate group between molecules.
15. Potential Energy
Also called stored energy, is the ability of a system to do work due to its position or internal structure
16. Reduction Reactions
In an oxidation-reduction reaction, reduction is the acceptance of electrons by a molecule. (reduction is gain of electrons).
17. Second Law of Thermodynamics
A law of nature stating that the spontaneous direction of energy flow is from more concentrated forms to less concentrated forms; with each conversion some energy is randomly dispersed in a form not as useful for doing work.

CHAPTER 6: Ground Rules of Metabolism

Before learning about metabolism it is important to review some basic concepts regarding ENERGY. What is the definition of energy? Ability to do work
It is important to note that, even though we may not fully understand energy’s true nature (is it a wave or a particle?) we do understand that energy can be converted from one form to another. Often, this is how we HARNESS energy!
There are two basic forms of energy:
A. POTENTIAL ENERGY is defined as energy that is stored. This can also be seen as the capacity to do work due to an object’s location or arrangement of parts.
1. The higher an object is above the ground the more energy it possesses. Think of jumping off of a chair verses jumping out of a plane; which would have a greater potential to do you bodily harm?
2. Another definition relates this energy to the structure of molecules and the type of bonds connecting the atoms together; hydrogen bonds have less energy than covalent bonds, so are easier to break. This form of energy is also called CHEMICAL energy and is the type we will be discussing in this class.
B. KINETIC ENERGY is defined as energy of motion. There are generally three types of kinetic energy:
1. LIGHT : The differrent colors of the rainbow ( R O Y G B I V ) have different levels of kinetic energy. “low” “high”
Red-orange-yellow light has low kinetic energy; blue-indigo-violet light has high kinetic energy.
2. SOUND: Different sounds both loudness and pitch (high or low) have different levels of kinetic energy. High volume or high pitched sounds with a high frequency have a high level of energy and can actually break glass
3. TEMPERATURE: Temperature is a number that is related to the average kinetic energy of the molecules of a substance. If temperature is measured in Kelvin degrees, then this number is directly proportional to the average kinetic energy of the molecules.
Heat is a measurement of the total energy in a substance. That total energy is made up of not only of the kinetic energies of the molecules of the substance, but total energy is also made up of the potential energies of the molecules.
So, temperature is not energy. It is, though, a number that relates to one type of energy possessed by the molecules of a substance. Temperature directly relates to the kinetic energy of the molecules. The molecules have another type of energy besides kinetic, however; they have potential energy, also. Temperature readings do not tell you anything directly about this potential energy. http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html
2. THERMODYNAMICS is the study of energy transformations that occur in matter .
A. There are several laws that govern energy conversions:
1.First LAW of THERMODYNAMICS (law of energy conservation) states that the total amount of energy in the universe is constant (can’t be created or destroyed).
a. it can be transferred or moved from one object or location to another, for example a cold metal chair gets warm after we sit on it for awhile.
b. it can also be transformed or changed from one form to another, for example the stored energy in wood is changed to light and heat as the wood burns
2. Second LAW of THERMODYNAMICS states that energy tends to flow from concentrated to less concentrated areas.
a. In other words, chemical reactions are never 100% efficient; some energy will always be “lost” to the surroundings as heat when chemical bonds break. As chemical reactions occur in the human body, about 60% of the potential energy becomes heat.The molecules in the surrounding area are moving more rapidly and therefore are becoming less organized.
b. Entropy_ is a measurement of how much and how far a concentrated form of energy has been dispersed after an energy change has occurred.
c. It takes energy to stay organized (orderly). Without energy input any system will tend to become more disorganized; large polymers will ultimately break down to become monomers.
3. Answer the following True-False statements. If the statement is false, make it correct by changing the underlined word and writing the correct word in the answer blank.
1. Energy that is stored in the bonds between atoms (chemical energy) is also called kinetic energy. F Chemical
2. Energy is the capacity to accomplish work, or to move objects. T
3. The amount of low-quality (heat) energy in the universe is decreasing. F Increasing
4. The entropy of two atoms decreases when a bond forms between them. T
5. No energy conversion can ever be 100 percent efficient, some of the stored energy will always be converted to heat. T
6. The collective strength of chemical bonds resists the spontaneous direction of energy flow. T
7. The second law of thermodynamics states that the total amount of energy in the universe is remaining constant. F First
4. Metabolism involves all the chemical reactions by which cells acquire and use energy as they synthesize (make), store, degrade (break down) and eliminate substances. There may be many molecules involved in an overall chemical reaction from start to finish.
A. Reactants (substrates) are substances that enter a reaction or are present at the beginning of the reaction.
B. Intermediates are the substances that form before a reaction ends somewhere along the way from the beginning of the process to the end of the process.
C. Products_ are the final substances that are produced by a chemical reaction, or are left at the end of a reaction pathway.

5. Chemical reactions in our bodies either store, release or transfer energy.
A. ENDERGONIC REACTIONS are those
that require an input of energy. If the
energy input is in the form of heat it is
called an ENDOTHERMIC reaction.
These reactions generally start with many
small molecules with fewer bonds and
therefore with a lower energy and join
them together to form larger molecules
that contain more bonds and therefore
have more energy. Energy must be added__
to create these additional bonds.
1. Photosynthesis is an example of an endergonic reaction; energy from the sun is used to combine CO2 and H2O to form glucose C6H12O6.
2. Joining together amino acids to form protein molecules is another example.

1. EXERGONIC REACTIONS are those

that release energy. If the energy released
is in the form of heat it is called an
EXOTHERMIC reaction. These reactions
generally start with one large molecule and
break it apart to form many smaller molecules
that contain fewer bonds and therefore have
less energy. Energy is released to the
surrounding area in the form of heat as the
chemical bonds are broken.
1. Burning a candle or a piece of wood is an example of an exothermic reaction. All the stored energy in the cellulose (glucose molecules) is released quickly in the form of heat and light.
2. Cellular Respiration is the chemical breakdown of glucose slowly, involving many steps to produce ATP and is also an example of an exothermic reaction.
C. Endothermic and Exothermic reactions can be illustrated as an “energy hill” where the reactants of the chemical reaction either start at the bottom of the “hill” or at the top of the “hill”. Draw “energy hill” diagrams for an endothermic and exothermic reaction to illustrate whether energy is released when the reaction occurs or energy must be added for the reaction to occur.
ENDOTHERMIC EXOTHERMIC

D. The molecule ATP generally couples the energy input with the energy output in chemical reactions. Cells try to use the energy from EXERGONIC reactions to drive the ENDERGONIC reactions.
1. Covalent bonds are very strong, so as they are broken the stored, potential (chemical) energy is released.
2. ATP however has even more potential
energy than what is stored in the covalent
bonds. The three phosphate groups are
surrounded by negative charges due to the
electrons surrounding the oxygen atoms.
Remember that similar charges tend to repel
each other; therefore there is an added
potential energy that is released as each
of these phosphate groups is removed by a hydrolysis reaction. ATP (AdenosineTRIphosphate) becomes ADP (Adenosine DI phosphate) and stored potential energy is released.
3. Phosphorylation Reaction _ is the transfer of a phosphate group from one molecule (like ATP or ADP) to another molecule.
6. Classify each of the following reactions as either endergonic or exergonic.

_1. Exergonic Burning of wood in a campfire.
_ 2. Endergonic The products of a chemical reaction have more energy than the reactants (starting materials) had originally.
_ 3 Exergonic. Glucose + oxygen → carbon dioxide + water + energy
_ 4.Exergonic The reactants (starting materials) of a chemical reaction have more energy than the products produced.
_ 5.Exergonic The reaction releases energy in the form of heat to the surrounding area.
_ 6.Endergonic CO2 + H2O + solar (UV) energy → Glucose + oxygen

7. Many substances in a cell possess a large amount of stored energy, are quite reactive and break down easily; however, they also require an initial amount of energy to start the chemical reaction. What is ACTIVATION ENERGY? Activation energy is the minimum amount of energy required for a reaction to proceed from reactant-product.

8.Enzymes are catalysts that can
speed up chemical reactions hundreds to millions of
times faster than without the help of the catalyst.
Without them, most chemical reactions that occur in
the body would not occur fast enough to satisfy the
needs of the cell.
A. Most enzymes are which type of organic molecule?
Proteins
B. Each enzyme is very specific for a specific molecule
(substrate) or type of molecule.
C. Enzyzmes do NOT change the original amount of
stored energy (potential energy) of the reactants
of the reaction.
D. Enzymes work by changing the amount of activation energy needed by the reactants to overcome the activation energy barrier and enter a chemical reaction.
In other words, enzymes lower_ the activation barrier that normally prevents the reaction from occurring. The amount of original potential energy in the reactants, the potential energy in the products and the overall energy of the reaction does NOT change, only the speed (rate) of the reaction changes.
E. The same enzyme works in both forward and reverse reactions. The direction of the reaction is determined by the concentration of the reactants and products and the amount of energy available NOT the enzyme itself.
F. During chemical reactions, the enzymes are NOT chemically changed to a different molecule; they remain unchanged at the end of the reaction, unlike the reactants (substrates) which are broken down and can be used again and again.

G. Enzymes work on the molecular level by following several different mechanisms, either alone or in combination.
1. Some enzymes help substrate_ molecules (reactants) get together (match-maker). If left on their own it is unlikely the molecules will collide with each other, so the enzyme attracts the substrates.
2. Some enzymes hold substrate molecules in a correct conformation_ (position) that favors a reaction. If left on their own, it is unlikely that the functional groups of the molecules will be in the correct positions to react with each other.
3. Some enzymes work by shutting out H2O. This often lowers the activation energy of a reaction. Remember that water tends to cause a “hydrolysis reaction” that causes bonds to break, not to form.
4. Some enzymes help the substrate by inducing_ a fit that helps to allow the substrate in to the active site, but then push it into place so the reaction can procede.
5. Some enzymes promote an acid-base environment which further encourages the loss of water and a dehydration synthesis reaction to occur so bonds can form between the substrate molecules.
H. Most enzymes require assistance or help from other molecules including:
1. Co-enzymes (also known as VITAMINS) are organic molecules that help enzymes speed up chemical reactions. Niacin (B3) for example helps in the metabolism of carbohydrates, lipids and proteins for energy.
2. Co-factors (also known as MINERALS) are inorganic or metal ions that also help enzymes. Ca+2 for example is needed to help break peptide bonds during the digestion of protein molecules and helps to form blood clots.
I. As mentioned, enzymes are very specific for a specific reactant or group of reactants. Enzymes are generally very large protein
molecules with a specific 3-dimensional shape. Part
of the enzyme serves as the “attachment site”, the
location where the substrate molecule or molecules
attach to the enzyme. This area is commonly called
the _Active SITE of the enzyme.
Describing enzyme function this way is often called the
“Lock and Key Model”. This means that the enzyme
and substrate work like a key in lock on a door, where
only a specific key will work on a specific lock.
J. In some cases, once the reactant or reactants attach
to the active site of an enzyme, the enzyme changes
its shape to better hold the substrate(s) in place while
the chemical reaction occurs. Describing enzyme
function this way is often called the
_ Inducing fit MODEL.
K. Once the chemical reaction is completed, the enzyme releases the new molecule formed (product) and is free to be used over and over again.
L. Enzyme activity can change with changes in the cellular environment.
1. Changes in :Temperature
a. For a reaction to occur quickly, the substrate molecules
(reactants) must come in direct contact with the active
site of the enzyme. Changing the speed that molecules
in solution move about may increase or decrease the
likelihood that the two molecules will “find” each other.
- increasing the temperature will generally cause the
molecules to move faster, increasing the reaction rate
- decreasing temperature will generally cause molecules to move slower, decreasing the reaction rate
b. Enzymes are protein molecules; any change in the
overall 3-D shape of the protein may change the
effectiveness of the enzyme. Increasing the temperature
weakens hydrogen bonds that help hold the 3-D shape,
thus alters the effectiveness of the enzyme.
c. Most human enzymes work best at normal body temperature of 35-40 oC.
2. Change in PH
:
a. The presence of hydrogen ions may
interfere with the hydrogen bonds
stabilizing the protein 3-D structure,
thus may result in a change in the protein
structure and therefore its function.
b. Most human enzymes work best at a
pH of 6-8, however enzymes in the
stomach work best at a pH of 1-2.
3. Changes in ions_concentrations (salinity):
a. Most enzymes stop working effectively when the solution is “saltier” or less salty than they can tolerate. Remember that a salt is a compound that when dissolved in water produces both positive (+) and negative (-) ions. Too much or too little salt can also interfere with the hydrogen bonds that hold the enzyme in the correct shape.
b. Most human enzymes work best at a salinity of 0.85%
4. When a protein molecule (or in this case an enzyme) has a change in the 3-D
structure causing it to lose its function, it is said to be denaturation_.



M. Many factors influence what an enzyme molecule does at any given time or whether it is produced in the first place. Enzyme inhibitors are important regulators of chemical reactions in the cell. In some cases, the product of a chemical reaction acts as an inhibitor of the enzyme required to start the reaction. When enough product is produced, the cell can stop the production of any more product by binding a product molecule to the enzyme preventing the reaction
from continuing. This is generally called allosteric INHIBITION.









There are two methods whereby enymes by be inhibited or prevented from performing their actions.
1. COMPETITIVE INHIBITION: this occurs when
molecule that resembles the reactant (substrate)
specific for an enzyme is present in solution and
binds to the active site before the reactant has a
chance to do so. This prevents the reaction from
occurring. Increasing the concentration of the
reactant will help speed up the reaction as it gives
the substrate a better chance of getting to the active
site before the inhibitor. An example of this type of
reaction is seen with the competative nature of carbon
monoxide with oxygen for hemoglogin in the blood.
Both molecules have a very similar molecular structure.
2. NONCOMPETITIVE (ALLOSTERIC) INHIBITION:
this occurs when a molecule attaches to the enzyme
molecule at some place other than the active site,
but in doing so changes the “shape” of the active
site so the reactant can no longer attach. This also
prevents the reaction from occurring. In this case
increasing the concentration of the reactant will
NOT help speed up the reaction since it still will not
be able to bind to the enzyme.



9. CELLULAR METABOLISM is defined as the sum of all chemical reactions that build up larger molecules from smaller ones and those that break down larger molecules into smaller ones releasing energy in the process.
















A. Biosynthetic Pathways (also known as ANABOLISM) involve the “building up” of larger molecules from smaller ones and requires
the input of energy (_ENDOTHERMIC).
B. _DEGRADATIVE Pathways (also known as CATABOLISM) involve the “breaking down” of larger molecules into smaller ones and
releases energy (EXOTHERMIC).
C. Many chemical reactions are “reversible” meaning the direction the reaction proceeds is based on the concentration of the reactants and products. If there are more reactants the reaction will move “forward”; if there are more products than reactants, then the reaction will tend to reverse and move “backward” breaking down the products and reforming the reactants. The reaction will continue until “equilibrium” (the rate of the forward and reverse reactions are equal) is reached.
10. Some chemical reactions that release or absorb energy do not use ATP as a
driving force; instead they involve the transfer of ELECTRONS. These
reactions are called _ OXIDATION- REDUCTION Reactions.
A. The removal or loss of electrons is called OXIDATION
B. The addition or gain of electrons is called _REDUCTION_

11. Match each of the following descriptions to the correct term.

1. F_ intermediates 2. G_ degradative pathways 3. I_ chemical equilibrium 4. D_ cofactors 5. J_ transport proteins 6. A_ metabolic pathway 7.E _ reactants (substrates) 8. C_ energy carriers 9. _B biosynthetic pathways 10. _H enzymes

A. An orderly series of reactions catalyzed by enzymes B. Metabolic pathway where small organic molecules are assembled into larger organic molecules in a series of reactions C. Mainly ATP; donate(s) energy to reactions D. Small molecules and metal ions that assist enzymes or serve as carriers E. Substances able to enter into a reaction F. Compounds formed between the beginning and end of a metabolic pathway G. Metabolic pathway where organic compounds are broken down in a series of reactions H. Proteins (usually) that catalyze reactions I. Rate of the forward reaction equals the rate of the reverse reaction J. Membrane-bound substances that adjust concentration gradients in ways that influence the direction of metabolic reactions

12. Which contains more potential energy, a large complex molecule like a protein, or the smaller amino acid subunits of which it is composed? Why?
large complex molecules hold a large amount of potential energy in their chemical bonds. When these bonds break down these macromolecules, we release a lot of energy which can be used to perform work.



13. Is the joining together of amino acids to form a protein an exothermic or endothermic reaction? Why?

Endothermic reaction, reactants have less energy than the products.


14. Where does the cell obtain energy to carry out endothermic reactions?
ATP, from performing exothermic reactions which release energy, and then the energy is used to perform reactions that require energy.

Sample Test Questions for chapter 6:

1. Kinetic energy differs from chemical energy in that
a. kinetic energy is stored energy that has the potential to do work, and chemical energy is the energy of movement
b. kinetic energy depends on the movement of atoms, whereas chemical energy depends on the movement of molecules
c. kinetic energy can be converted into various forms of energy, whereas chemical energy can only be converted to heat
d. kinetic energy is the energy of a moving object, whereas chemical energy is the potential energy stored in chemical bonds.
e. chemical energy is a particular form of kinetic energy

2. TRUE or FALSE: According to the second law of thermodynamics, energy can neither be created nor destroyed.

3. What percent of energy obtained from food is lost as heat energy?
a. 100%
b. 60%
c. 40%
d. 25%

4. Where is energy stored in a molecule?
a. in the nucleus
b. in the mitochondria
c. in glycogen
d. in bonds

5. What are the three parts that make up an ATP molecule?
a. adenine, ribose, 3 phosphate
b. adenine, thymine, 3 phosphate
c. adenine, glucose, 3 potassium
d. adenine, glucose, 3 phosphate

6. During enzyme catalyzed reactions, a substrate is another word to mean
a. end product
b. enzyme
c. reactant
d. all of the above

7. The active site of an enzyme
a. is where the coenzyme is attached
b. is a specific bulge or protrusion on an enzyme
c. is a place on the enzyme where substrate molecules attach
d. is less active than other parts of the enzyme

8. TRUE or FALSE: Most of the cell’s enzymes are classified as carbohydrates.

9. Some enzymes involved in the hydrolysis of ATP cannot function without the help of inorganic molecules called minerals. In this case the minerals function as
a. substrate molecules
b. cofactors
c. coenzymes
d. non-competitive inhibitors
e. competitive inhibitors

10. A substance that binds to a site other than the active site and in the process changes the shape of the active site on the enzyme is called a(n)
a. competitive inhibitor
b. non-competitive inhibitor
c. enzyme deactivator
d. co-enzyme

11. TRUE or FALSE: Reactions that are part of a “biosynthetic pathway” (anabolism) are generally described as being exothermic reactions.

12. TRUE or FALSE: Reduction reactions involve a gain in electrons.